For an optical tracking system, due to the limited sampling rate and time delays in the image-based tracking loop, control bandwidth is usually restricted. An optimized controller based on Youla–Kucera parameterization is proposed to improve both vibration rejection and target tracking performance. This optimized controller combined the position error signal and the control output to compensate for the original feedback loop. The performance in low frequency was enhanced using an optimized Q31-filter, although the close-loop bandwidth of the tip-tilt mirror was not improved. The stability and robustness of this control configuration were analyzed by gain margin and phase margin of the open-loop transfer function. Because of relying on a simple and low-frequency model of the tip-tilt mirror control system, this new controller did not lead to a compromise between vibration rejection and noise propagation in the loop. Simulations and experiments were used to testify to the effectiveness of the new controller.
For an image-based tracking loop system of tip-tilt mirror, the traditional control methodologies mainly include a single-position loop or two-position loop. The most effective method for enhancing tracking performance is to increase control gain for a high bandwidth. However, the image sensor sampling rate and time delay engendered by data processing restricts the bandwidth. Therefore, a position-rate control method is proposed to improve the performance of a tip-tilt mirror control system. The angular rate of tip-tilt mirror is calculated from the angular position measured by the linear encoder. The open-loop rate transfer function of tip-tilt mirror features differential in the low-frequency domain because the original tip-tilt control system is zero-type. When the inner rate feedback loop is implemented, an integrator is introduced into the original position loop. A PI (proportional-integral) controller can stabilize the position loop such that two integrators are in the tracking loop, so the low-frequency performance can be improved compared to the original control method. The experimental results coincide with the theoretical analysis and then verify the correctness of the presented theories.
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